I did the 5/16 about two months ago and love it. In combination with the CAI and exhaust, it's like I'm driving a different car. I bought my FX in 04, but didn't start modding until a year ago, so I have really been able to feel the changes each mod makes.
My research shows that the 5/16 is best for NA while the 1/2 is better if you plan to go FI eventually. Of course, I have not tried the 1/2 in my car to be able to compare, but I went with the basic 5/16 kit - no lower plenum gasket - and I love the gains it gave me.
My research shows that the 5/16 is best for NA while the 1/2 is better if you plan to go FI eventually. Of course, I have not tried the 1/2 in my car to be able to compare, but I went with the basic 5/16 kit - no lower plenum gasket - and I love the gains it gave me.